Melt Promise margarine in a large pot over medium-high heat. Add
the sweet potatoes, brown sugar, salt, pepper, and water; bring to a
simmer. Reduce the heat to medium, cover, and cook, stirring often,
until the sweet potatoes are tender (a fork should pierce a cube with
very little resistance), 45 to 60 minutes.

Preheat oven to 350°. When the sweet potatoes are tender, use a
slotted spoon to transfer the potatoes a greased 9-inch baking dish.
Bring the sauce in the pot to a rapid simmer over medium-high heat.
Continue simmering until sauce has reduced to a glaze, 7-10 minutes.
Pour over sweet potatoes in baking dish and top with marshmallows. Bake
for 10 minutes.

Turn broiler to high and continue baking until tops of marshmallows
have browned and puffed. Remove from oven and serve immediately.